// Copyright (c) Acrosync LLC. All rights reserved.
// Free for personal use and commercial trial
// Commercial use requires per-user licenses available from https://duplicacy.com

package duplicacy

import (
	"fmt"
	"io"
	"math/rand"
	"net"
	"os"
	"path"
	"runtime"
	"strings"
	"time"
	"sync"

	"github.com/pkg/sftp"
	"golang.org/x/crypto/ssh"
)

type SFTPStorage struct {
	StorageBase

	client          *sftp.Client
	clientLock      sync.Mutex
	minimumNesting  int // The minimum level of directories to dive into before searching for the chunk file.
	storageDir      string
	numberOfThreads int
	numberOfTries   int
	serverAddress   string
	sftpConfig      *ssh.ClientConfig
}

func CreateSFTPStorageWithPassword(server string, port int, username string, storageDir string,
	minimumNesting int, password string, threads int) (storage *SFTPStorage, err error) {

	authMethods := []ssh.AuthMethod{ssh.Password(password)}

	hostKeyCallback := func(hostname string, remote net.Addr,
		key ssh.PublicKey) error {
		return nil
	}

	return CreateSFTPStorage(false, server, port, username, storageDir, minimumNesting, authMethods, hostKeyCallback, threads)
}

func CreateSFTPStorage(compatibilityMode bool, server string, port int, username string, storageDir string, minimumNesting int,
	authMethods []ssh.AuthMethod,
	hostKeyCallback func(hostname string, remote net.Addr,
		key ssh.PublicKey) error, threads int) (storage *SFTPStorage, err error) {

	sftpConfig := &ssh.ClientConfig{
		User:            username,
		Auth:            authMethods,
		HostKeyCallback: hostKeyCallback,
	}

	if compatibilityMode {
		sftpConfig.Ciphers = []string{
			"aes128-ctr", "aes192-ctr", "aes256-ctr",
			"aes128-gcm@openssh.com",
			"chacha20-poly1305@openssh.com",
			"arcfour256", "arcfour128", "arcfour",
			"aes128-cbc",
			"3des-cbc",
		}
		sftpConfig.KeyExchanges = [] string {
			"curve25519-sha256@libssh.org",
			"ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
			"diffie-hellman-group1-sha1", "diffie-hellman-group14-sha1",
			"diffie-hellman-group-exchange-sha1", "diffie-hellman-group-exchange-sha256",
		}
	}

	serverAddress := fmt.Sprintf("%s:%d", server, port)
	connection, err := ssh.Dial("tcp", serverAddress, sftpConfig)
	if err != nil {
		return nil, err
	}

	client, err := sftp.NewClient(connection)
	if err != nil {
		connection.Close()
		return nil, err
	}

	for storageDir[len(storageDir)-1] == '/' {
		storageDir = storageDir[:len(storageDir)-1]
	}

	fileInfo, err := client.Stat(storageDir)
	if err != nil {
		return nil, fmt.Errorf("Can't access the storage path %s: %v", storageDir, err)
	}

	if !fileInfo.IsDir() {
		return nil, fmt.Errorf("The storage path %s is not a directory", storageDir)
	}

	storage = &SFTPStorage{
		client:          client,
		storageDir:      storageDir,
		minimumNesting:  minimumNesting,
		numberOfThreads: threads,
		numberOfTries:   8,
		serverAddress:   serverAddress,
		sftpConfig:      sftpConfig,
	}

	// Random number fo generating the temporary chunk file suffix.
	rand.Seed(time.Now().UnixNano())

	runtime.SetFinalizer(storage, CloseSFTPStorage)

	storage.DerivedStorage = storage
	storage.SetDefaultNestingLevels([]int{2, 3}, 2)
	return storage, nil
}

func CloseSFTPStorage(storage *SFTPStorage) {
	if storage.client != nil {
		storage.client.Close()
		storage.client = nil
	}
}

func (storage *SFTPStorage) getSFTPClient() *sftp.Client {
	storage.clientLock.Lock()
	defer storage.clientLock.Unlock()
	return storage.client
}

func (storage *SFTPStorage) retry(f func () error) error {
	delay := time.Second
	for i := 0;; i++ {
		err := f()
		if err != nil && strings.Contains(err.Error(), "EOF") && i < storage.numberOfTries {
			LOG_WARN("SFTP_RETRY", "Encountered an error (%v); retry after %d second(s)", err, delay/time.Second)
			time.Sleep(delay)
			delay *= 2

			storage.clientLock.Lock()
			connection, err := ssh.Dial("tcp", storage.serverAddress, storage.sftpConfig)
			if err != nil {
				LOG_WARN("SFTP_RECONNECT", "Failed to connect to %s: %v; retrying", storage.serverAddress, err)
				storage.clientLock.Unlock()
				continue
			}

			client, err := sftp.NewClient(connection)
			if err != nil {
				LOG_WARN("SFTP_RECONNECT", "Failed to create a new SFTP client to %s: %v; retrying", storage.serverAddress, err)
				connection.Close()
				storage.clientLock.Unlock()
				continue
			}
			storage.client = client
			storage.clientLock.Unlock()
			continue
		}
		return err
	}
}
// ListFiles return the list of files and subdirectories under 'file' (non-recursively)
func (storage *SFTPStorage) ListFiles(threadIndex int, dirPath string) (files []string, sizes []int64, err error) {

	var entries []os.FileInfo
	err = storage.retry(func() error {
		entries, err = storage.getSFTPClient().ReadDir(path.Join(storage.storageDir, dirPath))
		return err
	})
	if err != nil {
		return nil, nil, err
	}

	for _, entry := range entries {
		name := entry.Name()
		if entry.IsDir() && name[len(name)-1] != '/' {
			name += "/"
		}

		files = append(files, name)
		sizes = append(sizes, entry.Size())
	}

	return files, sizes, nil
}

// DeleteFile deletes the file or directory at 'filePath'.
func (storage *SFTPStorage) DeleteFile(threadIndex int, filePath string) (err error) {
	fullPath := path.Join(storage.storageDir, filePath)
	var fileInfo os.FileInfo
	err = storage.retry(func() error {
		fileInfo, err = storage.getSFTPClient().Stat(fullPath)
		return err
	})
	if err != nil {
		if os.IsNotExist(err) {
			LOG_TRACE("SFTP_STORAGE", "File %s has disappeared before deletion", filePath)
			return nil
		}
		return err
	}
	if fileInfo == nil {
		return nil
	}
	return storage.retry(func() error { return storage.getSFTPClient().Remove(path.Join(storage.storageDir, filePath)) })
}

// MoveFile renames the file.
func (storage *SFTPStorage) MoveFile(threadIndex int, from string, to string) (err error) {
	toPath := path.Join(storage.storageDir, to)
	var fileInfo os.FileInfo
	err = storage.retry(func() error {
		fileInfo, err = storage.getSFTPClient().Stat(toPath)
		return err
	})
	if fileInfo != nil {
		return fmt.Errorf("The destination file %s already exists", toPath)
	}
	err = storage.retry(func() error { return storage.getSFTPClient().Rename(path.Join(storage.storageDir, from),
		path.Join(storage.storageDir, to)) })
	return err
}

// CreateDirectory creates a new directory.
func (storage *SFTPStorage) CreateDirectory(threadIndex int, dirPath string) (err error) {
	fullPath := path.Join(storage.storageDir, dirPath)
	var fileInfo os.FileInfo
	err = storage.retry(func() error {
		fileInfo, err = storage.getSFTPClient().Stat(fullPath)
		return err
	})
	if fileInfo != nil && fileInfo.IsDir() {
		return nil
	}
	return storage.retry(func() error { return storage.getSFTPClient().Mkdir(path.Join(storage.storageDir, dirPath)) })
}

// GetFileInfo returns the information about the file or directory at 'filePath'.
func (storage *SFTPStorage) GetFileInfo(threadIndex int, filePath string) (exist bool, isDir bool, size int64, err error) {
	var fileInfo os.FileInfo
	err = storage.retry(func() error {
		fileInfo, err = storage.getSFTPClient().Stat(path.Join(storage.storageDir, filePath))
		return err
	})

	if err != nil {
		if os.IsNotExist(err) {
			return false, false, 0, nil
		} else {
			return false, false, 0, err
		}
	}

	if fileInfo == nil {
		return false, false, 0, nil
	}

	return true, fileInfo.IsDir(), fileInfo.Size(), nil
}

// DownloadFile reads the file at 'filePath' into the chunk.
func (storage *SFTPStorage) DownloadFile(threadIndex int, filePath string, chunk *Chunk) (err error) {
	return storage.retry(func() error {
		file, err := storage.getSFTPClient().Open(path.Join(storage.storageDir, filePath))

		if err != nil {
			return err
		}

		defer file.Close()
		if _, err = RateLimitedCopy(chunk, file, storage.DownloadRateLimit/storage.numberOfThreads); err != nil {
			return err
		}
		return nil
	})
}

// UploadFile writes 'content' to the file at 'filePath'.
func (storage *SFTPStorage) UploadFile(threadIndex int, filePath string, content []byte) (err error) {

	fullPath := path.Join(storage.storageDir, filePath)

	dirs := strings.Split(filePath, "/")
	fullDir := path.Dir(fullPath)
	return storage.retry(func() error {

		if len(dirs) > 1 {
			_, err := storage.getSFTPClient().Stat(fullDir)
			if os.IsNotExist(err) {
				for i := range dirs[1 : len(dirs)-1] {
					subDir := path.Join(storage.storageDir, path.Join(dirs[0:i+2]...))
					// We don't check the error; just keep going blindly
					storage.getSFTPClient().Mkdir(subDir)
				}
			}
		}

		letters := "abcdefghijklmnopqrstuvwxyz"
		suffix := make([]byte, 8)
		for i := range suffix {
			suffix[i] = letters[rand.Intn(len(letters))]
		}

		temporaryFile := fullPath + "." + string(suffix) + ".tmp"

		file, err := storage.getSFTPClient().OpenFile(temporaryFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC)
		if err != nil {
			return err
		}

		reader := CreateRateLimitedReader(content, storage.UploadRateLimit/storage.numberOfThreads)
		_, err = io.Copy(file, reader)
		if err != nil {
			file.Close()
			return err
		}

		err = file.Close()
		if err != nil {
			return err
		}

		err = storage.getSFTPClient().Rename(temporaryFile, fullPath)
		if err != nil {
			if _, err = storage.getSFTPClient().Stat(fullPath); err == nil {
				storage.getSFTPClient().Remove(temporaryFile)
				return nil
			} else {
				return fmt.Errorf("Uploaded file but failed to store it at %s: %v", fullPath, err)
			}
		}

		return nil
	})
}

// If a local snapshot cache is needed for the storage to avoid downloading/uploading chunks too often when
// managing snapshots.
func (storage *SFTPStorage) IsCacheNeeded() bool { return true }

// If the 'MoveFile' method is implemented.
func (storage *SFTPStorage) IsMoveFileImplemented() bool { return true }

// If the storage can guarantee strong consistency.
func (storage *SFTPStorage) IsStrongConsistent() bool { return true }

// If the storage supports fast listing of files names.
func (storage *SFTPStorage) IsFastListing() bool {
	for _, level := range storage.readLevels {
		if level > 1 {
			return false
		}
	}
	return true
}

// Enable the test mode.
func (storage *SFTPStorage) EnableTestMode() {}